1. Field of the Invention
This invention relates to a technique for high-sensitivity high-precision imaging and size reduction of an imaging apparatus used for a dry image recording system.
2. Description of the Related Art
Imaging apparatus for obtaining diagnostic hard copy images by digital radiography using storage phosphor imaging plates, CT imaging, MR imaging, etc. have adopted a wet system wherein a silver salt photographic material is exposed and wet-processed.
On the other hand, a dry system recording apparatus involving no wet chemical processing has recently engaged attention. Light-sensitive and/or heat-sensitive heat-developable photographic materials or heat-developable photographic films (hereinafter inclusively referred to as heat-developable light-sensitive materials) are used in a dry system recording apparatus. In a dry system recording apparatus, a heat-developable light-sensitive material is irradiated (scanned) with a laser beam to form a latent image in an image exposure section, brought into contact with a heating means to perform heat development in a heat development section, and discharged out of the apparatus.
The dry system is advantageous in that image formation completes in a shorter time than in a wet system and that the issue of waste liquid disposal is not involved, and is fully expected to enjoy an increasing demand.
Heat-developable light-sensitive materials that have been used in a conventional dry system have a silver halide spectrally sensitized to the infrared or red region. However, spectrally sensitized heat-developable light-sensitive materials undergo desensitization during storage due to gradual decomposition of the spectral sensitizers with time.
JP-A-12-305213, filed by the same applicant as the present invention, suggests that the problem is settled by exposing a silver halide which is not spectrally sensitized to an ultraviolet to blue laser beam. Nevertheless, the method disclosed failed to design a sufficiently sensitive system and was insufficient for assuring necessary image quality, i.e., sharpness.
An object of the present invention is to provide a method and an apparatus for image formation which achieve high-density high-precision imaging or system size reduction compared with conventional apparatus by using a high-iodide silver halide light-sensitive material having high image quality and high sensitivity to an ultraviolet to blue laser beam.
The present invention provides, in an aspect, an image forming method comprising exposing a heat-developable light-sensitive material comprising a support having thereon at least a light-sensitive silver halide having a silver iodide content of 5 to 100 mol %, a light-insensitive organic silver salt, a heat developing agent, and a binder by means of a scanning optical system having a light source emitting a laser beam having an emission peak between 350 nm and 450 nm to form a latent image on the heat-developable light-sensitive material, heating the heat-developable light-sensitive material to about 80 to 250xc2x0 C. in a heat development section, and cooling the heat-developable light-sensitive material having been heat treated in the heat development section to or below a development stopping temperature while the heat-developable light-sensitive material is transported in a cooling section
The image forming method of the invention includes an embodiment wherein the silver halide of the heat-developable light-sensitive material exhibits a direct transition absorption ascribed to the silver iodide crystal structure.
The present invention also provides, in another aspect, an image forming apparatus comprising:
an image exposure section having a scanning optical system including a laser light source emitting a laser beam having an emission peak between 350 nm and 450 nm, in which a heat-developable light-sensitive material is imagewise exposed to form a latent image,
a heat development section in which the heat-developable light-sensitive material having the latent image is heated to about 80 to 250xc2x0 C., and
a cooling section in which the heat-developable light-sensitive material having been heat treated in the heat development section is cooled to or below a development stopping temperature.
The image forming apparatus according to the invention includes the following embodiments:
1) The scanning optical system is composed of the laser light source, a polarizer for polarizing the laser beam from the laser light source, and a plurality of optical elements for directing the laser beam from the polarizer to the heat-developable light-sensitive material.
2) The laser light source has an emission peak between 390 nm and 430 nm.
3) The laser beam is from a semiconductor laser.
4) The laser light source has a plurality of lasers, and laser beams from the respective lasers are superposed.
5) The laser light source has a plurality of lasers having their oscillation wavelengths set different so that the respective beams reflected from the heat-developable light-sensitive material may offset against each other, and the plurality of beams are superposed to have approximately the same wavelength.
6) The laser beam is directly modulated to form a gray scale latent image on the heat-developable light-sensitive material.
7) The laser beam is modulated by an acoustic optical modulator to form a gray scale latent image on the heat-developable light-sensitive material.
8) At least one of the optical elements is an aspherical optical element.
9) The laser beam has a beam diameter of about 20 to 150 xcexcm on the surface of the heat-developable light-sensitive material.
10) The heat development section has:
at least two heaters which are fixedly arranged along the moving direction of the heat-developable light-sensitive material and impart a heat treatment at a prescribed temperature to the heat-developable light-sensitive material,
a delivering means for sliding the heat-developable light-sensitive material downstream on each of the heaters, and
a pressing means for pressing at least part of the heat-developable light-sensitive material, while being delivered, onto the surface of the heaters.
11) The temperatures of the heaters are individually controlled.
12) At least one of the heaters which is the most upstream in the heat development section is divided into at least three portions across the width direction of the heat-developable light-sensitive material, and the temperatures of the at least three portions are individually controlled.
13) The heat development section has:
a heat drum which imparts a heat treatment at a prescribed temperature to the heat-developable light-sensitive material being transported on the heat drum and
a pressing means for pressing the heat-developable light-sensitive material onto the surface of the heat drum.
14) The heat-developable light-sensitive material is vertically delivered while being scanned with the laser beam in the fast-scan direction.
15) The cooling section has a heat conductive roll by which the heat-developable light-sensitive material is delivered.
16) The cooling section has a heat conductive belt which cools the heat-developable light-sensitive material to or below a development stopping temperature while conveying the heat-developable light-sensitive material.
17) The cooling section has a plurality of rollers between which the heat-developable light-sensitive material is transported and meanwhile cooled to or below a development stopping temperature, and the rollers in the downstream half of the cooling section cool the heat-developable light-sensitive material to or below the glass transition temperature of the base of the heat-developable light-sensitive material.
18) The cooling section comprises a plurality of cooling rollers arranged on both sides of the heat-developable light-sensitive material in an alternate configuration.
19) The image forming apparatus has a density correction system comprising a density measuring section for measuring the density of a heat-developed image on the heat-developable light-sensitive material and a density correction calculating section which detects a density difference between the density data of the developed image measured in the density measuring section and recorded image density signals and calculates image signals to be sent to the image exposure section or heat energy to be applied to the heat development section based on the density difference thereby to make density correction.
The above-described constitution of the method and apparatus allows use of a heat-developable light-sensitive material which is capable of forming a high quality image with high sensitivity by blue laser exposure. Accordingly, high-output small-size semiconductor lasers having short wavelengths of around 400 nm can be utilized for exposure, which brings about the following advantages. Applied to an apparatus of conventional size, the system of the present invention allows a beam to be converged to a smaller diameter, which enables imaging with higher density and higher precision. The beam size being equal, on the other hand, the optical pass length (focal length) can be made shorter, which allows remarkable size reduction of optical equipment.